The present invention relates to the field of orthodontics, and more particularly to the field of orthodontic supplies including brackets and adhesives.
Orthodontists move patients' teeth into desired positions by applying gentle, but constant force to the teeth. As much as two years of gentle force may be required to coax teeth into their proper positions. At present, the process may involve preparation of the teeth through application of a chemical etching agent such as phosphoric acid. Small metal, plastic or ceramic brackets are then bonded to the surface of the prepared teeth using a dental adhesive. The brackets are linked together with wire or other linkage such that forces can be transmitted in a controlled manner to the teeth.
Different adhesives have been used over the years. In the early 1960s, a first generation of adhesives used for orthodontic brackets was developed which relied upon straight epoxy resins. These adhesives proved generally unsatisfactory because of their slow set-up times of up to 30 minutes. In the late 1960's and 1970's, a second generation of adhesives came on the market. These adhesives relied upon a dimethylacrylate monomer, (Bisphenol A Diglycidyl Methacrylate, known in the art as Bis/GMA), which was cut with low viscosity diacrylate diluents such as Triethylene Glycol Dimethylacrylate (known in the art as TEGDM or TEGDMA). In the late 1970's a third generation of orthodontic adhesives known as "honeymoon" adhesives became available which utilized high molecular weight polymeric fillers and blends of mono- and dimethylacrylates. These adhesives require the orthodontist to brush a primer on the surface of the bracket and on the tooth. A higher viscosity paste is then placed on the bracket, and the bracket placed on the tooth. A fourth generation of adhesives were light curable and provided convenience of simplified application and reduced application times. Light curing enables the practitioner to take as long as needed to position the bracket, and then rapidly fix it in place with a short exposure to UV, infrared, visible or some other wavelength or wavelengths of light.
Presently available light cured systems are generally based on Bowen's resin, which comprises Bis/GMA, TEGDMA, and inorganic filler particles, and was disclosed in Erickson et al, U.S. Pat. No. 4,163,004, issued Jul. 31, 1979. One example of such systems is TRANSBOND (.TM.) sold by MINNESOTA MINING AND MANUFACTURING CO. (.TM.). Another example is LIGHT BOND (.TM.) manufactured by RELIANCE ORTHODONTICS (.TM.). In such systems, a practitioner typically prepares an adhesive on an "as needed" basis. The prepared adhesive is applied to a bracket, and the bracket-with-adhesive is positioned on an etched portion of the tooth. The adhesive is cured with the application of visible or UV light. The adhesives and brackets are purchased and inventoried separately. Several differently shaped and sized brackets are used to accommodate different teeth and orthodontic purposes. Typically, the brackets are constructed from various materials, including metal, ceramic, plastic, and combinations of these materials.
Although the above-described bonding system is an improvement over methods used thirty years ago, several problems remain. One problem is that the practitioner must typically prepare the adhesive by mixing two or more substances together. Since the adhesives may be workable for only a relatively short period of time, the mixing process may need to be repeated many times in a given day, resulting in considerable inconvenience. Also, since the exact proportions of the substances in the adhesive may vary from mixture to mixture, adhesive mixtures with sub-optimal properties may be produced. Still another problem is that the brackets are relatively small, and the process of dabbing adhesive onto the brackets may be inconvenient and may result in spattering of adhesive onto undesired areas of the bracket or the skin. Still another problem is that the bonding strength of currently available adhesives may be excessive when used with ceramic brackets. Still another problem is that the Bowen's resin may tend to become stained or discolored during use.